Files in ignored_paths affect the amount of heap needed by the type checker

ignored_paths seems to work correctly for ignoring files checked by the type checker, but it dosen't seem to be helping deal with large amounts of files being checked. By placing a large amount of junk data in an hhvm project, we can break the type checker similary to #7887.

### HHVM Version

```
HipHop VM 3.23.2 (rel)
Compiler: 1511206791_111660617
Repo schema: 57a6d72ee7a93fe666bcfd7e75d7e2e160e38911
```

### Standalone code, or other way to reproduce the problem
hello.php
```
/tmp/hh_server/zShomezSjayzSCodezStmpzShack-example-site.monitor_log <==
[2017-12-04 22:06:35] Could not load config at /etc/hh.conf, using defaults
Informant using dummy - resigning
[2017-12-04 22:06:35] Starting first server
[2017-12-04 22:06:35] About to spawn typechecker daemon. Logs will go to /tmp/hh_server/zShomezSjayzSCodezStmpzShack-example-site.log

[2017-12-04 22:06:35] Just started typechecker server with pid: 29072.
[2017-12-04 22:06:35] Got request for typechecker. Prior request 0.0 seconds ago
dmesg: read kernel buffer failed: Operation not permitted
[2017-12-04 22:06:36] check_and_run_loop_ threw with exception: File "utils/sys_utils.ml", line 125, characters 2-8: Assertion failed
[2017-12-04 22:06:37] check_and_run_loop_ threw with Unix.ECHILD. Exiting

==> /tmp/hh_server/zShomezSjayzSCodezStmpzShack-example-site.log <==
Called from file "procs/multiWorker.ml", line 77, characters 31-52
Called from file "list.ml", line 88, characters 24-34
Called from file "third-party/core/core_list.ml", line 192, characters 22-47
Called from file "procs/multiWorker.ml", line 87, characters 20-70
Called from file "server/serverInit.ml", line 973, characters 4-43
Called from file "server/serverInit.ml", line 1043, characters 2-19
Called from file "server/serverMain.ml", line 437, characters 19-39
Called from file "server/serverMain.ml", line 36, characters 14-67
Called from file "server/serverMain.ml", line 551, characters 12-74
Called from file "server/serverUtils.ml", line 67, characters 6-10
```